Photoconductors are highly photosensitive in the visible region, and are widely used in various devices, such as copying machines, printers, etc. Most of the currently used photoconductors are produced by applying a photosensitive layer including an inorganic charge generating material selected from selenium, zinc oxide, cadmium sulfide and others as a main component to a conductive substrate. However, these inorganic charge generating materials are still unsatisfactory in photosensitivity, thermal stability, water resistance, durability and other physical properties required in copying machines and printers. For example, photoconductors using cadmium sulfide suffer from poor water resistance and durability, and photoconductors using zinc oxide have a problem in terms of low durability. Further, photoconductors using selenium and cadmium sulfide are limited in their production and handling.
In an effort to solve the problems of the inorganic charge generating materials, a great deal of research has been conducted on organic charge generating materials. Of these, oxytitanium phthalocyanine is widely used due to its superior photosensitivity, durability, thermal stability, etc.
Oxytitanium phthalocyanine is commonly synthesized by reacting 1,2-dicyanobenzene or 1,3-diiminoisoindoline as a main material with titanium tetrachloride or tetraalkoxy titanium as a titanium source in N-methylpyrrolidone, 1-chloronaphthalene or quinoline as a solvent at 160˜200° C. for 6˜12 hours, and purifying the obtained reaction product. The final product is strictly defined as “oxytitanium phthalocyanine in a crude state (hereinafter, referred to as an “oxytitanium phthalocyanine crude”)”. Japanese Patent No. 62-256865 describes a method for preparing an oxytitanium phthalocyanine crude by using 1,2-dicyanobenzene and titanium tetrachloride, U.S. Pat. No. 4,971,877 describes a method for preparing an oxytitanium phthalocyanine crude by using 1,3-diiminoisoindoline and tetraalkoxy titanium, and Bull. Chem. Soc. Jpn., 68, 1001-1005, 1995 reports a method for preparing an oxytitanium phthalocyanine crude by using 1,2-dicyanobenzene and tetrabutoxy titanium. Since the oxytitanium phthalocyanine crudes cannot be directly used as charge generating materials due to their large particle size and poor electrophotographic characteristics, they must undergo an appropriate post treatment process in order to be used as highly photosensitive charge generating materials. The structural formula of oxytitanium phthalocyanine is represented by the following Formula 1:

U.S. Pat. No. 5,164,493 discloses a process for the preparation of oxytitanium phthalocyanine as a charge generating material which comprises dissolving an oxytitanium phthalocyanine crude in a mixed solution of trifluoroacetic acid and methylene chloride, and reprecipitating the solution in a mixed solution of methanol and water. The charge generating material thus prepared shows X-ray diffraction peaks at Bragg angles of 7.2±0.2°, 8.9±0.2°, 14.3±0.2°, 18.0±0.2°, 23.9±0.2°, 25.6±0.2°, 27.3±0.2°, 28.8±0.2°, 29.4±0.2°, and 36.4±0.2°. However, this process has the following disadvantages: i) large quantities of toxic gases are released due to the use of trifluoroacetic acid, ii) troublesome steps are involved, and iii) the high cost of trifluoroacetic acid results in high production costs.
U.S. Pat. No. 5,252,417 discloses a process for preparing oxytitanium phthalocyanine as a charge generating material by using concentrated sulfuric acid, which is cheaper than trifluoroacetic acid. The charge generating material thus prepared shows X-ray diffraction peaks at Bragg angles of 7.2±0.2°, 9.1±0.2°, 11.2±0.2°, 13.5±0.2°, 14.4±0.2°, 24.0±0.2°, 27.2±0.2°, and 28.8±0.2°. According to this method, an oxytitanium phthalocyanine crude is dissolved in concentrated sulfuric acid in an amount of about 30˜50 times the amount of the oxytitanium phthalocyanine crude, and the resulting solution is recrystallized from a solution of methanol and water. However, since an excessive amount of the sulfuric acid is used, costs required for neutralization are increased. In addition, since the crude must be dissolved at a temperature not higher than room temperature, there is a limitation in reducing the amount of the sulfuric acid to be used due to increased viscosity.
U.S. Pat. No. 5,786,121 suggests a method for preparing oxytitanium phthalocyanine suitable as a charge generating material by mixing pentafluoropropionic acid and a halogenated alkane or halogenated aromatic compound, adding an aliphatic or aromatic sulfonic acid as an additive to the mixture to obtain an oxytitanium phthalocyanine crude, dissolving the oxytitanium phthalocyanine crude, and reprecipitating the solution in a mixed solution of water and methanol. However, since this method uses pentafluoropropionic acid, it produces much more toxic fumes than the method using trifluoroacetic acid. In addition, since the method uses difficult-to-handle and expensive raw materials, it is very dangerous and incurs considerable production costs.
Thus, there is a need for a method of preparing oxytitanium phthalocyanine usable as a high-quality charge generating material by using a cheap and easy-to-handle material, without the use of expensive and difficult-to-handle reactants, such as trifluoroacetic acid and pentafluoropropionic acid.